Vortex pumps in the crossing lattices regime of highly anisotropic layered superconductors

It is now well established that vortex dynamics in samples with a spatially asymmetric pinning potential can lead to rectifying vortex ‘diode’ behaviour. Spatial asymmetry is not a fundamental requirement for the control of vortex motion, however, and we demonstrate that vortex ‘lensing’ is possible in highly anisotropic layered superconductors simply under the action of non time-reversible trains of in-plane magnetic field pulses. Our devices depend crucially on the existence of ‘crossing’ pancake vortex (PV) and Josephson vortex (JV) lattices in Bi2Sr2CaCu2O8+δ (BSCCO) single crystals under tilted magnetic fields. An attractive interaction between these two sub-lattices makes it possible to indirectly manipulate the PV distribution by modifying the JV lattice, and a number of functional devices based on this principle have been proposed. In our experiments a BSCCO single crystal is placed on a Hall probe array, and cooled below Tc in a small out-of- plane magnetic field. Trains of sawtooth in-plane field pulses are then applied to the system and different elements of the Hall array used to demonstrate PV lensing or antilensing behaviour, depending on the pulse shape. The mechanism leading to lensing will be discussed and results compared with molecular dynamics simulations.